A new fossil of the Cretaceous dinosaur Psittacosaurus, a dog-sized herbivore with a parrot-like beak, that was donated to a Chinese university, came with a surprise — revealed only after scientists observed it under light ultraviolet.
It retained large areas of preserved skin, down to its cellular structure, providing new information about the evolution of skin in feathered dinosaurs. The fossil points to “zoned development” in the skin of these dinosaurs, the researchers said, with Psittacosaurus and probably other feathered dinosaurs having scaly, reptile-like skin in featherless regions of the body, and smooth, bird-like skin in areas with feathers.
“Initially, we didn’t have much hope of finding soft tissue because, to the naked eye, our specimen appeared to preserve only bone. We didn’t give up, however, because we knew that during fossilization soft tissue can be replaced by minerals, which can mix with the sediments,” said Zixiao Yang, postdoctoral researcher in paleontology at University College Cork, Ireland, and lead author. of the study published in May in Nature Communications magazine.
“When I turned on the UV light, I felt my heart almost stop. Large areas of scaly skin, covering his chest and belly, were glowing a stunning golden-yellow color under the UV light. The fossilized skin looked really exquisite, covered in small, rounded scales about a millimeter wide,” Yang said.
Soft tissue fossils are rare. Skin fossils of this quality are even rarer.
Unearthed in northeastern China, the nearly complete fossil, dated to approximately 130 million years ago, is of a juvenile Psittacosaurus about 66 cm long and approximately 3 years old when it died. It was donated in 2021 to Nanjing University from a private collection.
Psittacosaurus is an early member of the lineage of horned dinosaurs called ceratopsians, which later produced great beasts like Triceratops. Psittacosaurus itself did not have horns. Its name means “parrot lizard” based on its prominent beak, adapted for eating plants.
Many dinosaurs had feathers. In fact, birds evolved from small feathered dinosaurs. The first rudimentary feathers are believed to have evolved from reptilian scales nearly 250 million years ago in animals ancestral to dinosaurs and flying reptiles called pterosaurs.
Psittacosaurus had simple, bristle-like feathers on the top of its tail. The rest of its body was covered in scaly skin. The fossil was missing skin from the dinosaur’s feathered regions, but researchers believe these areas had bird-like skin.
“This discovery adds nuance to our understanding of feather evolution. The acquisition of modern bird-like skin occurred only locally on the body. Tough, reptile-like skin remained essential in regions of the body not protected by feathers,” said Maria McNamara, professor of paleontology at University College Cork and co-author of the study.
Bird skin exhibits multiple feather adaptations.
Birds have a dermal network of microscopic muscles that surrounds each feather and acts like a hydraulic system, including muscles that pull the feathers in different directions. There is also a network of smooth muscles under the skin that keeps the feathers separated, as well as deposits of fatty tissue anchored to the base of the skin that create an even skin surface and feather orientation. Furthermore, the feathers are connected by a system of sensory nerve fibers.
“Until now, we didn’t know whether skinned dinosaurs and their relatives evolved these skin adaptations first and feathers second, or whether they evolved at the same time, and on which parts of the body,” McNamara said.
The Psittacosaurus fossil “strongly suggests that the evolution of feathers — and the new skin adaptations — happened at the same time,” McNamara said.
The dinosaur’s scaly skin closely resembled the skin of today’s reptiles.
“They are similar in many ways, including the shape, size, arrangement and composition of skin cells, and the way the skin produces color patterns,” Yang said.
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